The unemployment insurance division, upon its own motion or upon application of an employing unit, may make a written determination with respect to whether an employing unit constitutes an employer, or whether services performed for or in connection with the business of an employing unit constitute employment, or both such determinations. A determination made pursuant to this section is final unless the employing unit, within fifteen calendar days of the date of mailing of the determination, files a written appeal with job service North Dakota.